1. Field of the Invention
The present invention relates in general to a novel process and apparatus for arc control in an electric arc furnace.
2. Description of the Prior Art
It is known that optimal performance of the melting and refining processes in arc furnaces requires rapid and accurate control of the arc. In fact, good arc stability is an important factor in the efficient use of power capacity, in limiting disturbances in the electric power system, and in reducing electrode wear.
In the melting period, the arc must be fed at full power, with good output, and must be reestablished very quickly after a failure or a short-circuit due to a very rapid displacement. In the refining period, penetration of the electrode into the bath must be avoided so as not to induce possible carburization; therefore, accurate control must be available. Finally, in periods of transition, i.e., in mixed solid-liquid phase, one is confronted simultaneously with the preceding constraints.
Up to the present time, adjustment of the arc has consisted of an adjustment of its impedance, or possibly its power, measured from its voltage and its current, by means of the displacement of the electrode or electrodes, which enables a great variation in the adjustment parameters. A major drawback of conventional devices using this method is that they use a combined pneumatic, hydraulic, mechanical, or electrical apparatus having non-negligible time constants and errors. Under these conditions, one must accept a compromise in arc control between speed and precision, both in the melting and refining periods.
Furthermore, arc stability is improved by accepting rather high line impedances, which reduce the power factor of the installation and thus its efficiency, due to the additional line losses which result.
The position of the arc is essentially variable as a function of:
the arrangement of the scrap iron before or during melting; PA1 the level of the liquid metal after melting; PA1 the wear of the electrodes. PA1 rapid direct control of the arc through the power supply; PA1 indirect control through the movement of electrodes, which is slow in continuous operation.
A high positioning of the electrodes, with a wide range of adjustment, is therefore indispensable in all cases.